1. Field of the Invention
This invention relates to the recognition of parts entering processing systems, and more particularly to the recognition of parts entering powder spray coating systems in order to control the spraying of the parts in a more efficient manner.
2. Description of the Prior Art
In electrostatic powder painting, products or parts to be coated are moved through an enclosure or booth where one or more spray guns spray the powder onto the products. The spray guns impart a charge to the powder particles, either triboelectrically or with a high voltage charging electrode. When the powder particles are sprayed from the guns, the particles are electrostatically attracted to the parts to be painted which are generally electrically grounded and which are typically suspended from an overhead conveyor or otherwise carried through the spray booth. Once these charged powder particles are deposited onto the parts, they adhere there by electrostatic attraction until the parts are subsequently conveyed into an oven where the particles are melted to flow together to form a continuous coating on the parts. Powder coating generally provides a tough and durable finish such as would be found on many appliances, garden furniture, lawn mowers, and many other products.
Recently, distributed control systems have been developed for powder coating systems which permit precise control of spray gun operations within the spray booth. An example of such a control system in shown in U.S. patent application Ser. No. 08/320,882, filed Oct. 5, 1994, and assigned to the assignee of the present invention. These control systems permit the development of a "recipe" for spraying each different individual part according to the configuration of the part and powder spraying needs applied to that part, so that the control system can position the spray guns, if necessary, and trigger the spray guns at the appropriate times. For example, if a part has a gap at a particular location, the control system can turn off the spray guns to reduce wasted powder. However, such control systems require an accurate and precise identification of the part or parts to be sprayed.
Several different approaches have been developed in a attempt to recognize precisely the parts in an automated spray coating system. One approach to parts recognition has been to provide an array of photo eyes or light curtains in vertical and horizontal directions at the entrance to the spray booth. These conventional photo eye or light curtain systems have a number of drawbacks, such as a very limited ability to provide appropriate part recognition information. While such systems may indicate the general size and shape of the parts entering the spray booth, in many cases the information is insufficient because it is necessary to recognize different part types which may have similar overall dimensions.
Another approach has been to provide sophisticated vision systems. Standard vision systems take a pixel-matrix view of an object and use standard filtering techniques to search for given features. If the features match, the part is recognized. These systems provide much better part recognition information, but they also have several serious disadvantages. First, the systems are very expensive due to the sophisticated optical recognition systems and required computing capabilities. Second, the systems require large computing capabilities, including large memory requirements, which are generally not present in most existing spray coating control systems.